1. Field of the Invention
This invention relates generally to a television receiver and, more particularly, to circuitry and a concomitant methodology for automatically determining if the predominant incoming signal to the receiver is an NTSC signal or an ATV signal, and then selecting the identified television signal for video/aural processing.
2. Description of Related Art
High-Definition Television (HDTV) provides received video images that have higher resolution and wider aspect ratio than standard National Television Systems Committee (NTSC) video images, even though both HDTV and NTSC are allocated the same 6 MHz frequency bandwidth. The improvement is fostered by digital signal processing techniques employed in HDTV. The term HDTV as now used in the literature has a connotation which encompasses the systems of equipment that generate and display images as well as the images themselves, including such characteristics and parameters as signal-to-noise ratio, colorimetry, and mitigation of the effects of spurious signals or interference. In addition, the term Advanced Television (ATV) collectively describes HDTV and variations on HDTV, such as Extended Definition Television (EDTV), which is a system that has less refined performance characteristics than HDTV; the terms ATV and HDTV are used interchangeably herein without loss of generality.
To avoid obsolescence of the literally millions of NTSC receivers currently in use, the Federal Communication Commission (FCC) has mandated that HDTV systems must operate concurrently with existing terrestrial broadcast ("over-the-air") NTSC systems until the year 2008 without causing interference to or receiving interference from NTSC systems. This two-pronged approach means that each television station will originate two channels--one that will transmit an NTSC signal for a given television program, and another transmitting an HDTV counterpart to that program. This arrangement for broadcasting HDTV signals via terrestrial propagation thereby intermixes HDTV signals with conventional NTSC signals. For instance, Channel 4 may be assigned to an NTSC signal carrying a given TV program, whereas Channel 38 may be assigned to the HDTV signal carrying the identical TV program. There are currently only 68 assigned channels for carrying 6 Mhz bandwidth television signals--12 in the Very High Frequency (VHF) band, and 56 in the Ultra High Frequency (UHF) band. Accordingly, it is quite conceivable that one of these 68 channels (e.g., as above, Channel 38) may be assigned to carry an HDTV program in one city, whereas this same channel may carry a completely different NTSC-UHF program in a second, nearby city.
For convenience to the consumer/viewer and, indeed, for enhancing marketability and acceptance of HDTV by the consumer, it is a virtual requirement for the commercial environment that the television receiver be able to automatically differentiate among NTSC, HDTV, or noise. For instance, in the second situation presented above, if a viewer's television receiver is located in the first city, then the viewer expects that Channel 38 will display the HDTV program to the viewer (along with, of course, the corresponding audio signal). On the other hand, a viewer in the second city expects the NTSC program of Channel 38 to be displayed on the receiver. For this differentiation between HDTV and NTSC to be especially beneficial and thereby engender consumer acceptance of HDTV, the differentiation technique should allow for an automatic, rapid selection by circuitry integral to the receiver so as to expeditiously present both the video and audio signals. Accordingly, for a receiver configured with either multiple tuners or even a single tuner that accepts both NTSC and HDTV signals, it would be extremely advantageous in gaining consumer confidence for the receiver to transparently and quickly present the desired information to the viewer. In addition, an automatic circuit will allow for rapid channel changing by the viewer.
The art appears to be devoid of teachings or suggestions of how to differentiate among NTSC, HDTV, or noise using circuitry specially arranged for such purposes and which automatically effects rapid capture of the desired incoming signal.
Nevertheless, in order to detect and ultimately display the appropriate incoming signal, a receiver compatible with both NTSC and HDTV would typically be implemented with one demodulator for NTSC and another demodulator for HDTV since NTSC and HDTV each operate on different signal processing principles, with the former being analog and the latter being digital. Accordingly, one plausible but rudimentary technique for determining which type of signal is present would place substantial onus on the consumer--by requiring the consumer to alternately switch between the HDTV demodulator and the NTSC demodulator; by having the consumer view the respective displayed images to determine which intelligible signal, if any, is then present; and then by having the consumer make the ultimate selection of the incoming program based on the subjective determination. Another conjectured technique would only improve matters slightly in that the alternate outputs from each demodulator, as the viewer switches between demodulators, would be monitored by circuitry and, based upon measured parameters, a decision as to which is the predominant signal could then be accomplished, albeit semi-automatically. However, this technique would also possess the deleterious effect of still requiring viewer interaction, as well as a potentially distracting amount of time for the circuitry to acquire the information necessary to make an informed decision, during which time the TV screen displays no coherent information.
Therefore, a need exists in the art for a circuit that is capable of automatically differentiating between NTSC and HDTV signals without burdening the user or adversely affecting, to any noticeable extent (if at all), the quality of the displayed image.